Grails Date unmarshalling

Question

If I get the following json from a RESTful client, how do I elegantly unmarshal the java.util.Date? (Is it possible without providing (aka. hard-coding) the format, that's what I mean by elegantly...)

{
  "class": "url",
  "link": "http://www.empa.ch",
  "rating": 5,
  "lastcrawl" : "2009-06-04 16:53:26.706 CEST",
  "checksum" : "837261836712xxxkfjhds",
}

Answer 1

The cleanest way is probably to register a custom DataBinder for possible date formats.

import java.beans.PropertyEditorSupport;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class CustomDateBinder extends PropertyEditorSupport {

    private final List<String> formats;

    public CustomDateBinder(List formats) {
        List<String> formatList = new ArrayList<String>(formats.size());
        for (Object format : formats) {
            formatList.add(format.toString()); // Force String values (eg. for GStrings)
        }
        this.formats = Collections.unmodifiableList(formatList);
    }

    @Override
    public void setAsText(String s) throws IllegalArgumentException {
        if (s != null)
            for (String format : formats) {
                // Need to create the SimpleDateFormat every time, since it's not thead-safe
                SimpleDateFormat df = new SimpleDateFormat(format);
                try {
                    setValue(df.parse(s));
                    return;
                } catch (ParseException e) {
                    // Ignore
                }
            }
    }
}

You'd also need to implement a PropertyEditorRegistrar

import org.springframework.beans.PropertyEditorRegistrar;
import org.springframework.beans.PropertyEditorRegistry;

import grails.util.GrailsConfig;
import java.util.Date;
import java.util.List;

public class CustomEditorRegistrar implements PropertyEditorRegistrar {
    public void registerCustomEditors(PropertyEditorRegistry reg) {
        reg.registerCustomEditor(Date.class, new CustomDateBinder(GrailsConfig.get("grails.date.formats", List.class)));
    }
}          

and create a Spring-bean definition in your grails-app/conf/spring/resources.groovy:

beans = {
    "customEditorRegistrar"(CustomEditorRegistrar)
}

and finally define the date formats in your grails-app/conf/Config.groovy:

grails.date.formats = ["yyyy-MM-dd HH:mm:ss.SSS ZZZZ", "dd.MM.yyyy HH:mm:ss"]

Answer 2

Be aware that the new version of Grails 2.3+ supports this type of feature out of the box. See Date Formats for Data Binding

With that said, if you are forced to use a version of Grails prior to 2.3, the CustomEditorRegistrar can be updated using the following code to eliminate the deprecation warning, and also uses the @Component annotation, which allows you to remove / skip the step of adding the bean directly in resources.groovy. Also not that I changed the grails configuration property name to grails.databinding.dateFormats, which matches the property now supported in Grails 2.3+. Finally, my version is a .groovy, not .java file.

import javax.annotation.Resource
import org.codehaus.groovy.grails.commons.GrailsApplication
import org.springframework.beans.PropertyEditorRegistrar
import org.springframework.beans.PropertyEditorRegistry
import org.springframework.stereotype.Component

@Component
public class CustomEditorRegistrar implements PropertyEditorRegistrar {

    @Resource
    GrailsApplication grailsApplication

    public void registerCustomEditors(PropertyEditorRegistry reg){
        def dateFormats = grailsApplication.config.grails.databinding.dateFormats as List
        reg.registerCustomEditor(Date.class, new CustomDateBinder(dateFormats))
    }
}